Practice Essentials

Botulism is an acute neurologic disorder that causes potentially life-threatening neuroparalysis due to a neurotoxin produced by Clostridium botulinum. The 3 main clinical presentations of botulism are as follows:

Infant botulism

Foodborne botulism

Wound botulism

Signs and symptoms

More than 90% of patients with botulism have 3-5 of the following signs or symptoms:

Diagnosis

A mouse neutralization bioassay confirms botulism by isolating the botulinum toxin. Toxin may be identified in the following:

Serum

Stool

Vomitus

Gastric aspirate

Suspected foods

C botulinum may be grown on selective media from samples of stool or foods. Note that the specimens for toxin analysis should be refrigerated, but culture samples of C botulinum should not be refrigerated. Wound cultures that grow C botulinum suggest the presence of wound botulism.

Electromyography

Characteristic electromyographic findings in patients with botulism include the following:

Brief, low-voltage compound motor-units

Small M-wave amplitudes

Overly abundant action potentials

An incremental increase in M-wave amplitude with rapid repetitive nerve stimulation may help to localize the disorder to the neuromuscular junction.

Careful attention to peripheral and central intravenous catheters with regular site rotation to reduce the risks of thrombophlebitis, cellulitis, and line infections should be part of the patient’s supportive care.

Background

Botulism is an acute neurologic disorder that causes potentially life-threatening neuroparalysis due to a neurotoxin produced by Clostridium botulinum. The toxin binds irreversibly to the presynaptic membranes of peripheral neuromuscular and autonomic nerve junctions. Toxin binding blocks acetylcholine release, resulting in weakness, flaccid paralysis, and, often, respiratory arrest. Cure occurs following sprouting of new nerve terminals.

The 3 main clinical presentations of botulism include infant botulism (IB), foodborne botulism (FBB), and wound botulism (WB). Additionally, because of the potency of the toxin, the possibility of botulism as a bioterrorism agent or biological weapon is a great concern.
[1] For more information, see CBRNE – Botulism.

Infant botulism is caused by ingested C botulinum spores that germinate in the intestine and produce toxin. These spores typically come from bee honey or the environment. Most infants fully recover with supportive treatment; the attributed infant mortality rate is less than 1%. Improperly canned or home-prepared foods are common sources of the toxin that can result in foodborne botulism. Wound botulism results from contamination of a wound with toxin-producing C botulinum. Foodborne botulism and wound botulism occur predominantly in adults and are the focus of this article.

C botulinum is an anaerobic gram-positive rod that survives in soil and marine sediment by forming spores. Under anaerobic conditions that permit germination, it synthesizes and releases a potent exotoxin. Microbiologically, the organism stains gram-positive in cultures less than 18 hours old. The organism may stain gram-negative after 18 hours of incubation, potentially complicating attempts at diagnosis. On a molecular weight basis, botulinum toxins are the most potent toxins known.

Eight antigenically distinct C botulinum toxins are known, including A, B, C (alpha), C (beta), D, E, F, and G. Each strain of C botulinum can produce only a single toxin type. Types A, B, E, and, rarely, F cause human disease. Toxins A and B are the most potent, and the consumption of small amounts of food contaminated with these types has resulted in full-blown disease. During the last 20 years, toxin A has been the most common cause of foodborne outbreaks; toxins B and E follow in frequency. In 15% of C botulinum infection outbreaks, the toxin type is not determined. Toxins C and D cause disease in various animals. Type G toxin has been associated with sudden death but not with neuroparalytic illness. It was isolated from autopsy material from 5 patients in Switzerland in 1977.

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Pathophysiology

The mechanism of action involves toxin-mediated blockade of neuromuscular transmission in cholinergic nerve fibers. This is accomplished by either inhibiting acetylcholine release at the presynaptic clefts of the myoneural junctions or by binding acetylcholine itself. Toxins are absorbed from the stomach and small intestine, where they are not denatured by digestive enzymes. Subsequently, they are hematogenously disseminated and block neuromuscular transmission in cholinergic nerve fibers. The nervous, gastrointestinal, endocrine, and metabolic systems are predominantly affected.

Because the motor end plate responds to acetylcholine, botulinum toxin ingestion results in hypotonia that manifests as descending symmetric flaccid paralysis and is usually associated with gastrointestinal symptoms of nausea, vomiting, and diarrhea. Cranial nerves are affected early in the disease course. Later complications include paralytic ileus, severe constipation, and urinary retention.

Wound botulism results when wounds are contaminated with C botulinum spores. Wound botulism has developed following traumatic injury that involved soil contamination, among injection drug users (particularly those who use black-tar heroin
[2] ), and after cesarean delivery. The wound may appear deceptively benign. Traumatized and devitalized tissue provides an anaerobic medium for the spores to germinate into vegetative organisms and to produce neurotoxin, which then disseminates hematogenously. The nervous, endocrine, and metabolic systems are predominantly affected. Symptoms develop after an incubation period of 4-14 days, with a mean of 10 days. The clinical symptoms of wound botulism are similar to those of foodborne botulism except that gastrointestinal symptoms (including nausea, vomiting, diarrhea) are uncommon.

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Frequency

United States

In the United States, approximately 154 cases of botulism are reported annually to the Centers for Disease Control and Prevention (CDC). Infant botulism accounts for nearly 75% of all botulism cases.

The incidence of foodborne botulism is approximately 24 cases per year. The incidence of wound botulism is 3 cases per year. The incidence of infant botulism is 71 cases per year, with a mean age of 3 months.

Toxin A is found predominantly west of the Mississippi River. Toxin B is found most commonly in the eastern United States. Toxin E is found in northern latitudes, such as the Pacific Northwest, the Great Lakes region, and Alaska. The frequency of botulism in native Alaskans is among the highest in the world.
[3] Toxin E outbreaks are frequently associated with fish products.

International

Human botulism is found worldwide. Spores from C botulinum strains that produce type A or B toxins are distributed widely in the soil and have been found throughout the world. Toxin type B is commonly found in Europe. Toxin G was originally isolated in Switzerland.

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Mortality/Morbidity

Mortality rates vary based on the age of the patient and the type of botulism. Foodborne botulism carries an overall mortality rate of 5-10%. Wound botulism carries a mortality rate that ranges from 15-17%. The risk of death due to infant botulism is usually less than 1%.

The recovery period from botulism is often prolonged (30-100 d). Some patients demonstrate residual weakness or autonomic dysfunction for 1 year after the onset of the illness. However, most patients achieve full neurologic recovery. Permanent deficits may occur in those who sustain significant hypoxic insults.

Sex

Wound botulism is more common in males. Foodborne botulism has no sexual predilection.

Age

Foodborne botulism and wound botulism predominately occur in adults. The mean age of infant botulism is 3 months.